In the processing of petroleum hydrocarbons and feed stocks, such as petroleum processing intermediates, and petrochemicals and petrochemical intermediates, e.g., gas, oils and reformer stocks, chlorinated hydrocarbons and olefin plant fluids, such as deethanizer bottoms, the hydrocarbons are commonly heated to temperatures of 400.degree. C. to 550.degree. C., frequently from 200.degree. C. to 550.degree. C. Similarly, such petroleum hydrocarbons are frequently employed as heating mediums on the "hot side" of heating and heating exchange systems. In virtually every case, these petroleum hydrocarbons contain deposit-forming compounds or constituents that are present before the processing is carried out. Examples of these preexisting deposit forming materials are alkali and alkaline earth metal-containing compounds, such as sodium chloride; transition metal compounds or complexes, such as porphyrins or iron sulfide; sulfur-containing compounds, such as mercaptans; nitrogen-containing compounds, such as pyrroles; carbonyl or carboxylic acid-containing compounds; polynuclear aromatics, such as asphaltenes; and/or coke particles. These deposit-forming compounds can combine or react during elevated temperature processing to produce a separate phase known as fouling deposits, within the petroleum hydrocarbon. In all cases, these deposits are undesirable by-products.
In many processes, the deposits reduce the bore of conduits and vessels to impede process throughput, impair thermal transfer, and clog filter screens, valves and traps. In the case of heat exchange systems, the deposits form an insulating layer upon the available surfaces to impede heat transfer and necessitate frequent shut-downs for cleaning. Moreover, these deposits reduce through-put, which of course results in a loss of production capacity with a drastic effect in the yield of finished product. Accordingly, these deposits have caused considerable concern to the industry.
While the nature of the foregoing deposits defies precise analysis, they appear to contain either a combination of carbonaceous phases which are coke-like in nature, polymers or condensates formed from the petroleum hydrocarbons or impurities present therein and/or salt formation which are primarily composed of magnesium, calcium and sodium chloride salts. The catalysis of such condensates has been attributed to metal compounds such as copper or iron which are present as impurities. For example, such metals may accelerate the hydrocarbon oxidation rate by promoting degenerative chain branching, and the resultant free radicals may initiate oxidation and polymerization which form gums and sediments. It further appears that the relatively inert carbonaceous deposits are entrained by the more adherent condensates or polymers to thereby contribute to the insulating or thermal opacitying effect.
Fouling deposits are equally encountered in the petrochemical field wherein the petrochemical is either being produced or purified. The deposits in this environment are primarily polymeric in nature and do drastically affect the economies of the petrochemical process. The petrochemical processes include processes ranging from those where ethylene or propylene, for example, are obtained to those wherein chlorinated hydrocarbons are purified.
Other somewhat related processes where antifoulants may be used to inhibit deposit formation are the manufacture of various types of steel or carbon black.